The subject invention was not funded in any part by the United States Government. All rights are retained by the inventor for his sole use.
Large signage applications for front lit and back lit mediums have several objectionable features. Front lit signage may use high efficiency light sources such as metal halide or high pressure sodium high intensity discharge (HID) lamps so that the light output of these lamps is very efficient. However, in a front lit signage application, luminairs are positioned in a way that causes most of the light to be reflected away from the sign face and cause light pollution. Also HID lamps do not provide a high index of color rendering. Signage medium may have to be color balanced to be visually acceptable under daylight and artificial illumination times.
Traditional light boxes for large billboard size back lit displays eliminate the light pollution problem but have several inherent other limitations. Fluorescent light bulb technology is not the most efficient light source available. Access is required to the light box interior for bulb replacement and ballast replacement limiting the types and properties of illustrative mediums.
A signage system that has a face that can be lit from behind with a color balanced high efficiency light source that would not require the face to be removed for bulb replacement or luminaire maintenance is wanting. Numerous applications of remote light source for illumination are known. In most cases an optical fiber bundle is simply used to conduct the light from a light source to the remote location and the light is emitted from the open end of these fibers. It is desirable to have a large flat panel that emits light in a homogenous method over the entire surface of a flat panel.
A method to extract light from an edge lit flat panel has been the subject of prior patents. In this instance, it is desirable to emit light over the surface of a collection of light guides and extract light evenly along a given length of the guide rather than only at the guide""s terminating face. This special need has been recognized in the prior art and numerous approaches to the extraction of light at intervals from optical light guides or optical fibers have been proposed. Each of these proposals, however, has its specific shortcomings making the application impractical or limited to only few situations.
For instance, Orcutt in U.S. Pat. No. 4,422,719, proposes the extraction of light from a light guide by enclosing the wave guide within a transparent sleeve having an index of refraction greater than the index of refraction of the wave guide and embedding within the sleeve light-reflecting powders, or by providing other discontinuities such as cuts or air bubbles within the fiber core. This approach has a number of shortcomings. First, the light extraction rate along the guide declines monotonically (and quite rapidly) from the proximal end to the distal end. The higher index of refraction of the cladding causes conversion of core modes (light propagation mode) to cladding modes to occur at the proximal end or the composite guide, thus sharply depleting the beam intensity as the light traverses the full length of the guide. Furthermore, the use of particles and bubbles suspended within the cladding causes excessive absorption of the light in the transmitting medium (particularly the cladding itself). Orcutt attempts to overcome the lack of light extraction control by including in the core refracting discontinuities or xe2x80x9clight extractionxe2x80x9d cuts through the cladding to the core and spacing these as a function of the distance from the light source. This approach is difficult to implement and furthermore, creates a series of discrete light sources along the guide and does not allow for continuous light extraction.
Mori (U.S. Pat. Nos. 4,460,940, 4,471,412 and 4,822,123) uses discrete light diffusing elements on a light transmission element to extract light from said light guide. In U.S. Pat. No. 4,460,940, Mori uses convex or concave diffusing elements to extract light of a specific wavelength, and a set of discrete elements with increasing density (but constant thickness) toward the distal end of the transmitting medium to extract light (presumably all wavelengths) from the transmitting element.
In U.S. Pat. Nos. 4,471,412 and 4,822,123, Mori uses discrete light outlets on a light conducting member. In the former patent he uses discrete diffusing elements without consideration to their quantitative light extraction capabilities while in U.S. Pat. No. 4,822,123 he uses light scattering discrete elements and simply increases their number as he approaches the distal end of the light conductor. The disadvantages of Mori""s light extraction systems include discontinuity of the light sources in that the appearance of the device includes a plurality of concentrated light sources, and the great difficulty in correctly spacing and sizing the extraction elements to provide for controlled light extraction from the light guide. Furthermore, the manufacturing and assembly of the devices of Mori is awkward and costly.
Cheslek U.S. Pat. No. 4,765,701 also uses discrete elements to extract light from an optical fiber in conjunction with a panel. Cheslek uses angular recesses and does not provide for means to control quantitatively the light extraction, and as a result, the illumination from the downstream (distal) recesses is progressively lower.
Hed U.S. Pat No. 5,222,795 proposed a curve-linear tapering of the cross sectional area of a fiber optic and abrading or painting the flattened surface. Hed in U.S. Pat No. 5,836,669 then proposed the application or elongated triangular reflective stripes onto a plastic plate. The tapering of the fiber optics provided a one way illumination with a substantial amount of light that could not be extracted from the distal end of the tapered fiber perpendicular to the emitting plate face. The tapering of the fiber optics provided a one way illumination with a substantial amount of light that could not be extracted from the distal end of the tapered fiber perpendicular to the emitting plate face. The painted triangle method does not allow enough emitting area to make the light emitted practical for general illumination. The light injection end in both these applications do not provide enough distance for an even light flux and would cause a bright spot at the injection end. This condition on Hed""s flat panel application is overcome by making the injection end part of the triangle very narrow and starting the installation of that triangle far from the emitting edge of the panel and thus further limiting the emitting surface.
Bousfeild U.S. Pat. No. 6,210,013, proposes a matrix of dots with increased diameters as they lay distal to the light injecting edge on a flat panel. This method is again limited by the actual area of reflectance
The prior art as described is a two dimensional light propagation over a flat panel and thus the light output is limited by the actual area of the reflecting coating or treatment. The Light Emitting Panel herein described uses irregular tapered tetrahedron grooves that have a surface area on at least two sides that is increased as it runs distal from the injection edge of the panel. The amount of light emitted is determined by the surface area and reflectance of the grooves and the treatment of the groove walls.
The prior art is impractical for use as a general illuminating system for task lighting or as an illumination system for large surface emission of light from a flat panel fed from a remote light source for billboard applications.
My present invention relates to the efficient generation, collection, concentration and transportation of light flux to a light emitting panel for signage applications. The light emitting panel provides controlled light extraction from light guides cast, imbedded or machined into base plastic or glass panels that are fed light from a remote source. Light is emitted from the panel from the surface of the light guides within the panel. The surface area of the light guides increases as they lay further from the light input end. The interior emitting surface of the light guides are treated to cause light refraction on their surface. Light is either emitted directly from the light guide surface through the face of the panel or from the reflected light from the back of the panel.
A tapered light guide that has the shape and size of the light flux transporting light pipe on one end and the shape and size of the light panel on the other end provides an area where light flux is arranged by total internal reflection to preserve the light flux etendue.
The subject invention was created to replace fluorescent lighting light boxes for back lit signage or applications with a remote light source device to overcome the space requirements, heat production, maintenance requirements, and application limitations of common light boxes for signage.
A principal object of the invention is to provide a homogeneous light emitting surface for backlight signage without having to access the area directly behind the light emitting surface for maintenance by creating a remote light source situation.
Another object is to provide a means to utilize efficient light sources to provide the light for the light emitting panel by the efficient collection and distribution of light flux from a HID light source and distribute the light evenly over a large light emitting surface.
Another object is to provide a means to blend the output of two or more HID lamp types and balance the color spectrum of the light emitted from the light panel to optimize the light emitting efficiency and emitted color.
Another object of the invention is to provide a method of and means for extracting light from an edge lit panel in a controlled manner so that drawbacks of earlier illuminating systems using other light guides are avoided. The panels are fabricated in sizes to take the place of fluorescent bulb light boxes. Once this method of light extraction was developed, large light sources could be coupled with large light pipes to generate and transport the light flux to a remote location.
Another object is to provide a lighting system where a high efficiency light source can be coupled to one or more light emitting panels without using traditional fiber optic bundles.
Another object is to provide a light pipe system that can transport large amounts of light flux to multiple locations from a single light source. The hollow light pipe is configured in a hexagonal or square prismatic shape that preserves the light source light flux etendue.
Another object is to provide a high efficiency light source that utilizes available high efficiency bulbs to generate light in the most efficient way possible without the limitations and light loss caused by concentration and heat when coupled to plastic light pipes.
It is yet another object of the invented system to provide a light source that may use several different light bulb types to mix the various light outputs of the various bulbs to render the desired color balance without filters or restrictions.
It is a further object of the invented system to utilize readily available high efficiency light bulbs of differing sizes and shapes to be concentrated into an output light flux that has a coherent wave front.
Another object is to provide a means to transport the light flux via a hollow tapered light pipe to concentrate and re-direct the light flux from the light source to the shape of the light panel without the use of fiber optics.
Yet another object is to create a complete remote light source backlit sign that can be configured into common sizes used by the signage industry that is efficient and desirable.